1. Field of the Invention
This invention relates to a method and universal conveying apparatus for automated inspection and classification of a variety of different product classes, while using a plurality of sensors interfaced to computer means for measuring different product features and separating same into predetermined categories. Following are some examples of product classes that can be conveyed, inspected and classified:
a. Spherical and spheroidal objects such as fruits and vegetables, ball bearings, billiard and bowling balls and the like.
b. Cylindrical objects such as cans, bottles, jars, drug capsules, cigarettes, ordnance shells, bullets, and the like.
c. Disc shaped objects such as wheels, gears, bottle or jar closure caps, round plates, cakes, precooked meals or pizzas in aluminum foil trays, tablets and the like.
d. Parallelepiped shaped objects such as boxes and containers (empty or with variously packaged items within), box-shaped various manufactured products, small appliances, components and parts.
e. Plate shaped objects such as electronic printed circuit boards.
f. Amorphous objects such as dates, berries, potatoes, avocado, soil clods, radioactive ore pieces, cookies, bread and other bakery products.
2. Description of Prior Art
Most existing automatic inspection machines are designed to classify or sort only a particular product class, and in most cases the classification is based on a single product feature. When more than one feature is used (usually less than three), they are addressed serially, one at a time, by one or several machines in a row. Of all products that can be efficiently inspected and classified by the machine disclosed hereby, sorting and sizing fresh fruits and vegetables is one of the most demanding and difficult tasks.
Color sorting machines for various specific fruits and vegetables, using yellow/green, red/green, blue/green etc. light reflectance ratios, have been used commercially for many years. The operating principle of these machines was based on optical filtration of reflected light, while the classification decision was performed by analog circuitry. Analog circuit color sorting is usually specific for each particular fruit type. It has largely been made obsolete by the introduction of digital image processing, such as in the machine disclosed herein, whereby color sorting is just one of several product features detected by reflected light, i.e. size, shape and surface blemishes.
The key component of any inspection machine, designed to sort a stream of objects in a mass production environment, is the conveying system. Its main function is to efficiently carry and present the inspected objects to the sensors. Three main types of conveying systems have been used hitherto in inspection machines based on computer vision:
a. Flat belt conveyors.
b. Cup conveyors.
The disadvantage of these conveyors is that the underside of the objects carried on them can not be seen by the camera. The flat belt conveyor has an additional deficiency since the exact placement of the objects on it is not known.
c. Roller conveyors, as in (1980 U.S. Pat. No. 4,221,297), which strive to overcome the above deficiencies by rapidly spinning spheroidal objects such as fruits, in front of a line scan camera.
Another popular way of presenting all sides of an object to a set of cameras is to view it simultaneously from different angles, as it free falls in a projectile like trajectory from one conveyor to another.
Inherent inaccuracy of this method stems from inconsistency of object orientation due to variability in sizes and shapes, while significant damage may be incurred by sensitive products, e.g. fruits and vegetables. Rapidly spinning a product in front of a line scan camera has essentially the same disadvantages, since it is very difficult to ascertain exactly one revolution view when the products vary in size and shape. Rapid spinning may also damage a delicate products.
The above conveying and inspection principles comprise "Reduction Sorting", whereby diversion mechanisms selectively deflect different product fractions form the main product stream, usually based on a single feature, e.g. color, blemishes, size etc. Even if more than one feature is inspected, it is done so serially by different machines, i.e. a color grading machine is followed by a sizing machine, while grading is mostly manual. The diversion mechanism is usually a solenoid operated baffle or an air stream blast. In most cases further inspection is required to finalize product grading according to other product features, by additional machines or human inspectors. In contrast, the machine disclosed hereby performs "Full Sorting" whereby several features of each and every piece are inspected, while a Bayesian type multiple feature decision-making algorithm may be used to optimally classify the product, whereupon it is deposited onto the appropriate side delivery conveyor. Needless to say that the former method is less cost effective.
The machine disclosed herein allows viewing and inspection of opposite sides of an objects at high speed by means of a pair of stacked cup conveyors and retaining grippers which hold the objects in place while they are turned around by an inverter wheel, as described in detail in the preferred embodiment of the present invention. This inversion apparatus is different and superior to the dual drum arrangement for capsule color sorting, as described in (1978 U.S. Pat. No. 4,082,188).
Another case in point is sorting by specific gravity, such as may be used for separating freeze damaged oranges from wholesome fruit, thick skinned fruit from thin skinned fruit, potatoes from soil clods etc. The machine disclosed herein can determine specific gravity of each inspected piece by its weight and volume, in conjunction with a plurality of other features.
In addition to the above product properties, it is sometimes also required to classify products by their mechanical or rheological properties. Thus a patent has been granted for an elaborate single feature machine which produces indentations on fruits for assessing their firmness, (1977 U.S. Pat. No. 4,061,020). Here again, the preferred embodiment of the present invention provides several superior means for measurement of mechanical properties of the inspected products, i.e. resistance to applied forces, contact pressure, frequency response or vibration damping characteristics and internal energy dissipation "on the go", without stopping the conveyor belt or reducing throughput speed.
In summary, we may cite the following deficiencies of commercially available inspection and classification machines:
a. The conveying apparatus of each machine is suitable for inspecting only a particular product class. This precludes cost effective standardized mass production, wherein adaptation to different products is only a matter of choosing the appropriate sensors and software package, while the structure of the machine and most of its mechanical parts remain the same.
b. While classifying only a specific product, the further restriction to one or at most two or three product features constitutes "Reduction Sorting", capable in most cases of performing only part of the entire sorting task, while the remainder is performed manually.
c. There is no provision for viewing both sides of an object while it rests upon a rapidly moving conveyor, enabling "Computer Vision Inspection" including reflected as well as transmitted radiation types, in conjunction with a plurality of other sensor systems.
d. There is no provision for accomplishing c. while handling the product gently, thereby minimizing potential mechanical damage to delicate products.
e. There is no means for physical contact with the inspected products "On-The-Go" whereby electrical connectors can be automatically attached to the product for functionality inspections.
f. There is no means for measurement of mechanical properties of inspected materials or products, wherein it may be important to measure resistance to applied forces, contact pressure, frequency response or vibration damping characteristics and internal energy dissipation, without stopping the conveyor or reducing throughput speed.